Evaluation of heat release and combustion analysis in spark ignition Wankel and reciprocating engine

In this study, a single-rotor multi side port Wankel research engine and a single cylinder spark ignition (SI) engine having three different type combustion chamber geometry (MR, Cylindrical bowl, Flat) were used. Engine experiments were performed at 2000 rpm, 3 bar and 5 bar bmep (brake mean effective pressure) and stoichiometric conditions. Combustion analysis was performed for Wankel and a reciprocating SI engine with three types combustion chamber geometries, which are not included in the literature. In the Wankel engine, the maximum pressure value was lower than the reciprocating SI engines and the maximum pressure obtained far away from the TDC. The reason of this is lower burning velocity and combustion progress toward the expansion stroke. Wankel engine's lower burning velocity also reduced the maximum temperature values. The normalized cumulative heat release rate was about 15% higher than the reciprocating SI engine with different combustion chambers. In Wankel engine, NO emissions are 15-45% lower due to the lower combustion temperatures. On the contrary, THC emissions were up to two times higher due to the combustion chamber geometry and absence of squish effect. The MR type combustion chamber has the highest combustion speed and pressure value due to the intense flow and mixture conditions. In the Wankel engine, combustion process is shifted toward the expansion phase, thus resulting to the lower thermal efficiency. In order to improve this process, additional precaution, such as different mixture formation and flow intensification methods in the combustion chamber are required.